Bonding in Sandwich Compounds

Abstract

A study is made of the bonding in sandwich compounds by means of ESR and susceptibility measurements. Data obtained for vanadocene and nickelocene are discussed in terms of various calculated MO schemes. The experimental results are compatible with the level order e2g ≲ a1g < e1g* for the highest-bonding and lowest-antibonding orbitals, all orbitals having a strong metal 3d character. The assignments given for the ground-state configurations are quantitatively checked by comparison of calculated and experimental D and g values. Both spin–orbit and spin–spin coupling are shown to give a substantial contribution to the value of D. The excitation energies used in the perturbation calculation of the DLS and g values are obtained from a ligand-field treatment of the low-energy bands in the optical absorption spectra.

Similar ligand–metal bonding for transition metals and actinides? 5f1 U(C7H7)2−versus 3dn metallocenes

“…For nickelocene, Ni 2+ (3d 8 ), the CF configuration is (3d σ ) 2 (3d δ ) 4 (3d π ) 2 and the GS is a spin-triplet . Note that the 3d-shell occupations are confirmed by experiments for both vanadocene 89 – 91 and nickelocene. 89 , 90 , 92 …”

“…Note that the 3d-shell occupations are confirmed by experiments for both vanadocene 89 – 91 and nickelocene. 89 , 90 , 92 …”

High-frequency and -field electron paramagnetic resonance of vanadium(IV, III, and II) complexes

“…The only relevant molecular complex that was studied early on was vanadocene (VCp 2 , bis( 5cyclopentadienyl)vanadium(II)), doped into a single crystal of ferrocene and investigated by conventional (22.5 GHz) EPR [136]. The value of D (0.83 cm -1 ) reported in this 1959 study was subsequently questioned by Prins et al [137,138] who obtained instead the value of |D| = 2.3…”

“…cm  by X-and Q-band EPR. The larger magnitude of D than typical for previously studied V II systems was attributed to arise from spin-orbit coupling (SOC) of the 4 A 2g ground state with the Edited Oct 30 23 low-lying 2 A 1g excited state [138]. This early controversy is still instructive as to the perils of using low-frequency/field EPR to investigate Kramers spin species with sizable zfs.…”

Zur paramagnetischen Elektronenresonanz metallorganischer Sandwich-Verbindungen, Teil I / The magnetic resonance properties of some sandwich compounds, part i

“…MO-Rechnungen der erweiterten Hückel-Methode schließen die Betrachtung von o-und ^-Orbitalen ein. Sie lieferten bei den von PRINS et al [6][7][8] untersuchten Verbindungen Vanadocen und Nickelocen brauchbare Resultate zur Erklärung der magnetischen Resonanzeigenschaften des Grundzustandes. Die aus ESR-Messungen gewonnenen Aussagen über den Orbitalcharakter und die Reihenfolge der höch-sten besetzten und niedrigsten unbesetzten Molekül -orbitale wurden in guter Übereinstimmung mit den Ergebnissen der theoretischen Berechnung gefunden.…”